The idea of a convoy at sea is a simple one – to put it in basic terms, there is safety in numbers, especially when a convoy of unarmed merchantmen is accompanied by a flotilla of warships.
Mariners have been making use of convoys for at least eight centuries, and the first Europeans to refine the concept were the Spanish, when their treasure fleets (which were established early in the 16th Century) sailed from the New World, bringing all manner of luxurious and novel booty.
Sailing individually, such ships could be picked off by pirates and enemy states, but a protected convoy presented a much tougher scenario for the average privateer – and the fact that convoys tipped the odds in favour of the merchants ships was often reflected in insurance premiums.
The Royal Navy honed its convoy tactics throughout the Napoleonic Wars – both protecting our own and attacking those of the enemy – and the chances of survival of single ships was so poor that there was no choice for a master but to join a convoys when crossing the ocean.
But the principles of the convoy system were largely ignored by the Admiralty at the start of World War 1 as they considered that fast, powerful battleships could wreak havoc with ocean-going convoys, standing off and firing long-range salvoes, potentially sinking several ships before the group managed to scatter.
If the Germans were to employ such tactics, the argument went, then the Admiralty would have to tie up valuable capital ships to protect the merchantmen, which was (in their eyes) a poor use of resources.
In fact, German surface raiders were to a greater extent holed up in friendly ports, and never got the chance to range across the oceans causing mayhem.
That was left to the submarines – and though they were relatively unsophisticated, and often little faster that the convoys with limited range, their success in the first three years of the war caused much dismay amongst Their Lordships.
There were, in fact, a number of different requirements for convoys between 1914 and 1918.
The first to be put into effect were the military convoys that brought troops from all over the Empire to serve in the European theatre – the first such major convoy left New Zealand in October 1914, with Japanese battlecruiser Ibuku protecting ten troopships as they made their way to Australia.
There a further 29 ships – a mix of merchant ships and troopships, accompanied by cruisers HMAS Melbourne and HMAS Sydney – joined the convoy and set course for Aden, with part of the voyage being covered by another Japanese cruiser Chikuma.
The Japanese continued to provide cover for troop and supply convoys from Australia and New Zealand throughout the war.
The most recognisable convoys of World War 1 were the ocean crossings, usually of the Atlantic, that were to become so familiar during World War 2, and it was the rising losses of these ships in U-boat attacks that cause the Royal Navy to rethink its plans.
Analysis of shipping movements in May 1917 revealed that the previous month had been the most costly of the war to date, with almost 400 Allied and neutral vessels being lost – a total of almost 900,000 tons, with an equally devastating death toll.
With the United States entering the war, and the consequent need to protect sea lanes busy with ships transporting vital troops and equipment destined for the Western Front, it was decided that convoys of (at first) up to 12 ships would be scheduled, but as confidence in the system grew that was increased to around 40, usually escorted by a cruiser, a clutch of destroyers and perhaps a dozen armed auxiliary ships such as trawlers.
Assembly points were designated along the eastern seaboard of North and South America, as well as for convoys originating in Africa, and the rapidly-implemented system was an instant success, with more than a million American soldiers safely crossing the Atlantic in the subsequent 18 months with the loss of just over 600 men in submarine attacks.
But the success in blunting the U-boat threat in the Atlantic and, to a lesser extent, in the Mediterranean caused the German navy to rethink its own plans, and they turned their fire on the crucial coastal shipping lanes and short sea crossings around the UK, often catching ships that had left their ocean-going convoys to disperse to various ports.
These were more difficult to protect and escorts were scarce, but in a move that hinted at the possibilities of air power – a vital factor in World War 2 convoys – such shipping was also organised into groups and given cover, at least in part, by aircraft and airships based ashore.
By contrast to the Great War, convoys were planned by the Allies from the earliest days of World War 2 and continued until the final days of conflict in the European theatre, which meant the Battle of the Atlantic raged from September 1939 until May 1945, by far the longest campaign of the war.
There was once again some reticence amongst Royal Navy hierarchy, with the same arguments being trotted out as had been rehearsed 25 years earlier, including a lack of suitable escort vessels, a reluctance to expose capital ships to such routine tasks, and the fact that – in some eyes – convoys were an inefficient system, with the convoy being limited to the best speed of the slowest ship in the group.
An early offensive tactic by the British saw hunting groups based on aircraft carriers, but their strike rate against U-boats was low, equipment was not yet up to the task and tactics were similarly rudimentary.
But it set the pattern for the Battle as a whole, as Germans honed their attacks on convoys and the Allies developed defensive (and later offensive) tactics, each side taking advantage of the shift in initiative until the enemy caught up.
Surface commerce raiders could do a great deal of damage, as was the case with convoy HX 84 (Halifax, Canada to Liverpool) in November 1940, when German heavy cruiser Admiral Scheer sank five merchantmen, and was only prevented from doing more damage by the brave sacrifice of armed merchant cruiser HMS Jervis Bay.
By the same token, a powerful escort force, maybe including a battleship, was known to force German raiders to retire rather than risk becoming engaged in a duel the were unlikely to win.
The loss of Bismarck in May 1941 had a sobering effect on the German command, and thereafter surface raiders featured far less prominently in the Battle of the Atlantic.
It was the scourge of the U-boat that took up most of the attention of Allied Naval planners and tacticians, particularly after the fall of France in 1940, after which U-boats were able to sail from bases on the Atlantic coast of France, extending their patrol range.
But Allied efforts to blunt their threat by using escort forces and extended range air patrols or carrier-borne aircraft started to pay dividends by 1942, and within a year or so the convoys themselves became part of the counterattack, as they proved irresistible to U-boats, which could then be destroyed by aggressive warships, either part of the convoy or as free-ranging special groups.
There were other advantages to convoys – if a U-boat attacked, it would often take hours to be in position to return to the fray as it would not have much of a speed advantage, and if during the attack it drew the attention of escorts, it would likely have to remain submerged in a bid to avoid detection, possibly for several hours, by which time the merchant ships would be many miles away.
As confidence in the system grew, larger convoys could be dispatched with some confidence, and the vast majority of ships involved never saw an enemy vessel – though the threat of attack was always present, which constantly preyed on the minds of military and commercial seafarers alike throughout the war, and thus throughout the Battle of the Atlantic.
Today’s image, from the Imperial War Museum collection (© IWM A 19734), shows U-boat killer sloop HMS Kite, pictured from escort carrier HMS Tracker, supporting an Atlantic convoy in October 1943. For more images search https://www.iwm.org.uk/collections
n This series is by no means a comprehensive review of the Battle of the Atlantic, which was a colossal clash – in terms of casualties alone more than 100,000 men are thought to have died as a direct result to the battle, and more than 4,000 vessels were sunk, while many times more those numbers were involved.
Instead, we have picked out some of the more important or thought-provoking features of the campaign, and would encourage you to read further on individual aspects such as eye-witness accounts from escort ships (both fiction and non-fiction) and the role of Enigma.
